*) Better performance (no interruption of airflow at all, but the gains against well designed butterflies are small)

*) More linear opening / torque response with pedal movement (barrels allow a small air gap, slowly getting bigger with rotation whereas butterflies open more on the circumference first, allowing a lot more air in with smaller rotation). This effect can be altered with the throttle linkage geometry, especially if there is a cam in the system.

Cons of barrels

*) The whole barrel rotates in the housing. Therefore the surface area of the 'sliding' surfaces is far greater, and it's away from the pivot access. The upshot is that they are a lot more susceptible to getting sticky with dirt ingress. In comparison butterflies have a small spindle, well shrouded from dirt.

*) Barrels can suffer from fuel pooling behind the barrel, that can suddenly be ingested when opening to fuel throttle. This can cause a hesitation on rapid throttle opening. Calibration can reduce this to an extent.

*) Barrels are usually more expensive

It is often mentioned that road cars, with higher dirt and less servicing, are well served with butterflies. Race cars are usually barrels.

My barrels have been on for 8 years and are only just being stripped, and have been fine.

Titan have now launched a range of butterfly throttles to compliment their barrels.

'Eagles may soar but weasles don't get sucked into jet engines' - David Brent